The present invention relates to an apparatus for pumping fluid and includes a pump unit and a hydraulic muffler which attenuates noise produced by the pump unit.
A known apparatus for use in pumping fluid is disclosed in U.S. Pat. No. 5,692,883. The apparatus disclosed in this patent includes a gear pump unit which is driven by an electric motor. A flexible duct is connected with the inlet to the gear pump unit. The flexible duct improves the absorption of sound waves generated by working of the gear pump unit. Another known gear pump unit is disclosed in U.S. Pat. No. 5,240,393.
A gear pump having a hydraulic muffler is disclosed in the aforementioned U.S. patent application Ser. No. 08/847,571 filed Apr. 24, 1997 by George M. Harpole, Michael B. Petch, and Nelson P. Mark and entitled "Hydraulic Power Steering System With Noise Attenuation". The apparatus disclosed in this application includes a gear pump having a fluid inlet and a hydraulic muffler. The hydraulic muffler attenuates noise by damping flow rate fluctuations that are caused by meshing gear teeth in the pump unit. The hydraulic muffler includes a compliant element and a conduit interposed between an inlet to the gear pump unit and a fluid reservoir.